The present invention relates to a refrigeration system and, more particularly, to a refrigeration system suitable for use in air conditioner of automobiles, having a fixed, pressure reducing device.
Hitherto, in the refrigeration system of the kind described, a capillary tube which interconnects the condenser and the evaporator of the refrigeration system plays also the role of the pressure reducing device. As the required flow rate of refrigerant is determined by the thermal load of the refrigeration cycle, the state of the refrigerant at the capillary tube inlet, such as degree of subcooling or dryness factor, is automatically determined by the flow-rate characteristic of the capillary tube. More specifically, if the flow rate of the refrigerant by weight is insufficient for the thermal load, the refrigerant is superheated as it flows through the evaporator toward the outlet of the latter, so that the liquid refrigerant in the accumulator is evaporated and moved into the condenser to enlarge the subcooling region in the condenser, resulting in an increased degree of subcooling of the refrigerant at the condenser outlet. Consequently, the flow rate of the refrigerant is increased to automatically achieve the balance of the cycle.
To the contrary, as the thermal load is decreased, the refrigerant at the evaporator outlet is partially liquefied and the refrigerant is stored in the accumulator. As a result, the subcooling region at the condenser outlet is reduced resulting in a smaller degree of subcooling at the refrigerant. As the thermal load is further reduced, the refrigerant comes to have a dryness factor x so that the flow rate of refrigerant is reduced to achieve the balance of the cycle.
As to this balance of the refrigeration cycle, it is well known that the refrigerant preferably is subcooled to some extent before it leaves the condenser, in order to obtain a large difference of enthalpy between the inlet and outlet of the evaporator. In the refrigeration system for air conditioners of automobiles, the fluctuation of thermal load is so large that the flow rate of the refrigerant changes widely. Namely, the refrigerant flows at an extremely large flow rate during heavy load operation, resulting in an extremely large degree of subcooling. This in turn requires a higher rate of discharge of heat from the refrigerant in the condenser and, hence, an extraordinarily high pressure of the outlet side of compressor, possible resulting in a discharge of refrigerant through a safety valve or reduction of performance due to the elevated pressure at the high pressure side of the refrigeration cycle.
Under these circumstances, there is an increasing demand for fixed flow restriction member having a flow rate characteristic which suits for large fluctuation of the flow rate and small rate of change of degree of subcooling.